As is well known, the electrolyte level in each cell of a lead-acid battery will diminish over a period of time. Evaporation and electrolysis eventually reduce the electrolyte to undesirably low levels. As the cells dry out, the battery becomes progressively less efficient until the dessicated battery finally cannot hold and deliver a charge, rendering it worthless.
Accordingly, the electrolyte level of the cells must be monitored at periodic intervals. After the electrolyte decreases to a predetermined level, distilled water must be introduced into each cell to replenish the supply of electrolyte. Care must also be exercised in order not to overfill each cell. An overfilled cell may prevent oxygen and hydrogen generated within the battery from safely escaping into the atmosphere. A build up of these gases may buckle the plates and possibly lead to an explosive condition. Moreover, spillage along the top surface of the battery may lead to a short circuit and/or speed the accumulation of deposits (primarily lead sulfate and lead carbonate) about the terminals thereby resulting in the degradation of battery performance.
It can be appreciated, therefore, that monitoring and servicing large arrays of lead-acid batteries is a labor intensive job. Oftentimes such batteries are left unattended for long periods of time. Even with the introduction of the new so-called "low maintenance" or "maintenance-free" battery alloys, it is expected that the cells will still require some attention.
Over the years, a number of topping-up systems have been developed. See for example, U.S. Pat. No. 1,361,437; No. 1,467,966; No. 3,052,745; No. 3,189,063; No. 3,550,651; No. 4,154,904 and U.K. Pat. No. 1,499,914.